This invention relates to improvements to redundant arrangements of sensors that measure physical quantities which may be represented by vectors. It also relates to the data management systems associated with these arrangements of sensors. The data management system portion of this invention accepts the signals to provide outputs that may be used to control the motion of a vehicle, such as an aircraft. Further, it provides malfunction detection and failure indication for the sensors.
Presently, aircraft and spacecraft with automatic flight control systems generally require reliable angular rate and translational acceleration information in three dimensions. Sensor systems containing redundant gyros and accelerometers, capable of operating satisfactorily after two component failures, are often provided to supply this information. In most cases where the vehicle maximum angular rate or translational acceleration requirement about one axis is different from the requirement about the other two axes, for example, maximum roll rate of 250.degree./sec; maximum pitch and yaw rate of 60.degree./sec; or maximum normal acceleration of 6 g's, and maximum lateral and longitudinal of 1 g, two different range gyros and accelerometers are used. To satisfy the redundancy and reliability requirements, multiple sensors of the same range with self contained electrical devices to detect sensor malfunctions are usually oriented with their sensitive axes (input axes) coaxial or "in-line" with one another. In cases where comparison monitoring for malfunction detection is also required, three or more sensors are provided. When comparison monitoring is employed, the output signal of each sensor is compared to the average of the outputs of the other two sensors. If the absolute value of the difference is greater than a fixed threshold, the sensor is considered failed.
Specifically, a two failure tolerant comparison monitoring malfunction detection requirement imposed on an aircraft rate gyro system has required large number of sensors, namely twelve of two different ranges. The sensors are arranged as follows: four of one range with their input axes coaxial with the aircraft roll axis and eight of a second range, four with their input axes coaxial with the aircraft pitch axis and four coaxial with the aircraft yaw axis.
Present comparison monitoring practices require that like sensors (e.g. roll gyros) be packaged on a rigid mounting surface in the vehicle so that structural vibration inputs to like sensors are the same. If like gyros are placed at different locations in the vehicle, the malfunction detection efficiency would be decreased because at different locations the structural vibration inputs to the sensors are dissimilar and change as a function of flight condition. The loss in efficiency results from the fact that the malfunction detection equations cannot distinguish between output signal differences due to sensor malfunctions and output signal differences due to dissimilar vibration inputs. In addition, it is desirable to locate sensors with respect to major structural bending nodes and antinodes of the vehicle. At the nodes and antinodes, the translational acceleration amplitude and the angular rate amplitude of vibration is minimized, respectively. Placement of sensors at or adjacent to these locations minimizes the need for output signal filtering. Output signal filtering and/or care in placement of the sensors is required to diminish regenerative interaction between the control system and structural bending. Regenerative interaction means that the control system in combination with the aircraft is unstable.
Unfortunately, these packaging and placement constraints, coupled with the multitude of sensors required to satisfy the redundancy needs, are inconsistent with the desirability of separating redundant sensors in spacecraft and aircraft to enhance the automatic control system equipment survivability. For example, in a combat situation, it is desirable to separate redundant components so that a single round of enemy fire does not destroy all components. Accordingly, it is an object of this invention to overcome and solve the packaging and sensor configuration problems.
In particular, it is an object of this invention to provide a configuration of sensors that satisfy the two failure tolerant/self-contained malfunction detection requirement and;
use the fewest number sensors
use like range (duplicate) sensors
provide a sensor system with improved malfunction detection capability, adequate output signal accuracy and an output signal replacement means that enhances system reliability
provide a configuration of sensors that can be dispersed to meet survivability requirements without (1) degrading failure detection efficiency, or (2) imposing requirements for special data handling (filtering).